(1) Field of the Invention
The present invention relates to a resin composition useful as a radiation curable resin composition, a thermosetting resin composition, and to a resin composition that has a low viscosity, a low shrink property and a rapid-curability, unlike a conventional curable resin composition.
(2) Description of the Related Art
Radical-polymerization type radiation curable resin compositions are utilized in the field of surface fabrication because they are rapidly curable at low temperatures, and the cured coating films have excellent scuff and chemical resistance. However, the radiation curable resin compositions, usually tend to have high viscosities at room temperature. Therefore, it is necessary to reduce the viscosities in order to facilitate their application.
The use of organic solvents or diluent monomers having low viscosities are necessary for viscosity reduction of the curable resin compositions. As a result, environmental concerns such as increased volatile organic compound (VOC) contents, skin irritation caused by the diluent monomers, along with the decreased curing rates of the resin compositions are observed.
In general, radiation curable resin compositions shrink remarkably in volume upon curing, therefore, a method comprising the addition of a high-molecular weight oligomer or polymer is adopted to reduce the percentage of shrinkage. However, when this method is adopted, the viscosity of the resin is increased; the coating properties are deteriorated; and further the coating curability is deteriorated by the decrease in resin concentration at the reaction site.
In the field of film coating materials, for example, radiation curable resin compositions draw attention. For instance, JP-A-3-252460 discloses a composition for coating material which comprises an ethylenic unsaturated compound having a molecular weight of 500 or less, a styrene-based polymer having a softening point of 70xc2x0 C. or higher, and a photopolymerization initiator which has excellent adhesive properties to various substrates, high gloss, blocking resistance, scratch resistance, water resistance, etc.
However, since the aforesaid composition contains a styrene-based polymer having no photo-reactivity, its viscosity becomes so high that the coatability is poor depending on the amount of the styrene-based polymer added. Moreover, since a large amount of the photopolymerization initiator must be incorporated into the composition in order to attain a high productivity, a large amount of the photopolymerization initiator remains in the cured coating film, resulting in a film product having the unpleasant odor of the photopolymerization initiator. Thus, a product having satisfactory overall performance characteristics could not be obtained.
In the field of coating materials for wood coatings, rapid-curing radiation curable compositions have come to be extensively used which entail a low energy cost and are good in productivity. Of these radiation curable compositions, those that contain an unsaturated polyester resin, inter alia, have been extensively used because they give a cured coating film that is excellent in finished appearance involving gloss and feeling of fleshiness, and they are inexpensive.
However, in the case of coating films having such a composition, the surface curing speed is lower than the in-depth curing speed, resulting in insufficient productivity of the applied and cured product. Moreover, since the internal strain of the cured coating film is increased by the cure shrinkage of one or more monomers and oligomers contained in the composition, the composition has the disadvantage in that the cured coating film tends to be cracked by repeated heating and cooling.
To overcome these problems, JP-A-4-202213 discloses a composition using a maleic acid-based unsaturated polyester containing a specific glycol component, and JP-A-5-202163 discloses a composition using an epoxy acrylate, a specific acryl polyol component and an isocyanate compound.
The composition disclosed in JP-A-4-202213 requires the use of styrene monomer as a diluent to improve the coating efficiency. The use of styrene monomer deteriorates the surface curability, however, and the work environment is harmed by odor from the volatilization of the styrene monomer. The composition disclosed in JP-A-5-202163 also fails to improve the work environment because it has a high viscosity and hence requires the use of a diluent, such as an organic solvent, to improve the coating work efficiency required for practical use.
In recent years, printing inks that can be cured by active energy rays such as electron rays, ultraviolet rays, visible rays, etc. have been increasingly substituted for common oil inks, because of their many advantages, such as faster printing and delivery, hygienic properties, etc. These printing inks comprise a composition containing a radical-polymerizable monomer, an oligomer and a coloring agent such as a pigment. As specific examples of the printing inks, the composition systems which also use in combination a diallyl phthalate-based polymer disclosed in, for example, JP-B-61-4861 and JP-A-3-212460 have been extensively used from the viewpoint of printability, curability, mar resistance, etc. These composition systems, however, involve the following problems. Since the diallyl phthalate-based polymer has no photo-reactivity, a photopolymerization initiator should be used in said composition systems in a larger amount than in composition systems composed of a radical-polymerizable monomer and an oligomer in order to attain a practical curing rate. In addition, when a large amount of the aforesaid diallyl phthalate-based polymer is added to control the polymerization shrinkage and improving the adhesive properties to a substrate, the viscosity is extremely increased, so that the printability, leveling properties, appearance and the like are deteriorated.
When the composition system disclosed is used as colored printing ink, its curing rate tends to decrease compared to an uncolored composition because of the remarkable light absorption by a dye or pigment for the coloring. Therefore, a larger amount of a photopolymerization initiator is necessary in order to attain a practical curing rate.
Moreover, when the amount of the photo-polymerization initiator is increased in order to improve the curability, the surface curability is improved, but the in-depth curability was not sufficient owing to remarkable light absorption in the surface layer, with the result that that the adhesive properties of the resulting coating film to a substrate are deteriorated.
Thus, it has been difficult to obtain all three conflicting characteristics, i.e., low viscosity, low shrink properties and rapid curability in a solvent-free radiation curable resin composition in all applications of the resin composition. To solve this problem, a method of foaming the resin composition during curing in order to prevent cure shrinkage, and a method of adding solid fine particles as disclosed in JP-A-7-228644, etc. have been proposed. These methods, however, have the disadvantage in that when the obtained resin composition is used as a coating material, the resulting cured coating film has an unsatisfactory appearance.
The reactive microgels disclosed in Japanese Patent No. 2703125 and JP-B-6-25210 are crosslinked fine particles with a small particle size and reactivity and, hence, do not undesirably influence the coating appearance, so they might be capable of solving the above problems. However, although these microgels are suitable for use inca resist composition for lithographic plates, they cannot achieve the low viscosity intended according to the present invention, for the following reason. The crosslinking density of particles of the microgel is so low that a solvent-free coating material cannot be obtained by mixing fine particles of the microgel with another radical-polymerizable monomer because the fine particles are swelled by the radical polymerizable monomer during mixing. The low viscosity was not obtained with these microgels.
Thus, conventional radiation curable resins cannot have all three characteristics: low viscosity, low shrink properties and rapid curability. Also during the production of a heat-cured coating film or a heat-cured molded article, there was a problem with achieving both a low viscosity and low shrink properties.
An object of the present invention is to provide a resin composition having all of the above-mentioned various properties at the same time and a crosslinked-fine-particle dispersion type curable resin composition using the aforesaid resin composition, by dispersing specific crosslinked fine particles in a radiation curable resin or a thermosetting resin composition.
The present inventors have found that all the three characteristics, low viscosity, low shrink properties and rapid curability can be obtained at the same time by dispersing crosslinked fine particles (A) obtained by polymerizing a compound (a1) having one or two radical-polymerizable ethylenic unsaturated groups in the molecule and a compound (a2) having three or more (meth)acryloyl groups in the molecule, in a compound (B) having at least one (meth)acryloyl group in the molecule.
That is, the present invention is a curable resin composition substantially free of water and solvents which is characterized by comprising
crosslinked fine particles (A) with an average primary-particle diameter in a range of 10 to 1,000 nm obtained by polymerizing a compound (a1) having one or two radical-polymerizable ethylenic unsaturated groups in the molecule and a compound (a2) having three or more (meth)acryloyl groups in the molecule, and
a compound (B) having at least one (meth)acryloyl group in the molecule.
The use of the crosslinked fine particles of the present invention enabled the same extent of shrinkage reduction with less viscosity increase compared to cases in which a conventional polymer or oligomer was incorporated. Moreover, the curing rate can be overwhelmingly increased. Therefore, unlike conventional radiation curable resin compositions, a curable resin composition can be obtained which satisfies all three characteristics, i.e., low viscosity, low shrinkage properties and rapid curability. Accordingly, the crosslinked fine particles are useful in various fields such as casting resins, coating materials, adhesives, inks, stereo lithography, photoresists, etc.
The components of the resin composition and crosslinked-fine-particle dispersion type resin composition of the present invention are explained below in detail.
In the present specification, the term xe2x80x9c(meth)acrylic acidxe2x80x9d means xe2x80x9cacrylic acid and/or methacrylic acidxe2x80x9d, and the term (meth)acryloyl group means xe2x80x9cacryloyl group and/or methacryloyl groupxe2x80x9d.
The crosslinked fine particles (A) which constitute the present invention are fine particles obtained by polymerizing a compound (a1) having one or two radical-polymerizable ethylenic unsaturated groups in the molecule and a compound (a2) having three or more (meth)acryloyl groups in the molecule. In the present specification, the crosslinked fine particles (A) refer to dried particles which are free of water and organic solvents.
The structure of the crosslinked fine particles (A) used in the present invention is not particularly limited and may be any of a single-layer structure, core/shell structure, laminated structure, etc.
The crosslinked fine particles (A) used in the present invention have the following characteristics not attained before: they cause only a slight viscosity increase when added to a dispersion medium component (B), and they decrease the polymerization shrinkage of the resin composition.
The component (a1) used for obtaining the crosslinked fine particles (A) is a compound (a1) having one or two radical-polymerizable ethylenic unsaturated groups in the molecule, and may be properly chosen in view of the purpose of use, required properties, etc. of the resin composition of the present invention.
Specific examples of the component (a1) include aromatic vinyl monomers such as styrene, xcex1-methylstyrene, xcex1-chlorostyrene, vinyltoluene, divinylbenzene, etc.; vinyl ester monomers such as vinyl acetate, vinyl butyrate, N-vinylformamide, N-vinylacetamide, N-vinyl-2-pyrrolidone, N-vinylcaprolactam, divinyl adipate, etc.; vinyl ethers such as ethyl vinyl ether, phenyl vinyl ether, etc.; acrylamides such as acrylamide, N-methylolacrylamide, N-methoxymethyl acrylamide, N-butoxymethyl acrylamide, N-t-butyl acrylamide, acryloylmorpholine, methylenebisacrylamide, etc.; (meth)acrylic acid; and (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, glycidyl (meth)acrylate, dimethylaminomethyl (meth)acrylate, diethylaminomethyl (meth)acrylate, benzyl (meth)acrylate, cyclohexyl (meth)acrylate, phenoxyethyl (meth)acrylate, tricyclodecane (meth)acrylate, allyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, isobornyl (meth)acrylate, phenyl (meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene grycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, neopentyl glycol hydroxypivalate di(meth)acrylic acid ester, polypropylene grycol di(meth)acrylate, bisphenol A polyoxyethylene di(meth)acrylate, hydrogenated bisphenol A polyoxyethylene di(meth)acrylate, hydrogenated bisphenol A di(meth)acrylate, cyclohexanedimethanol di(meth)acrylate, cyclohexanediol di(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, etc. Among these, preferred are (meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, ethylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, etc.
The above-exemplified compounds may be used either singly or in combination.
Next, the component (a2) used for obtaining the crosslinked fine particles (A) is a compound having three or more (meth)acryloyl groups in the molecule. This compound (a2) having three or more (meth)acryloyl groups has a high reactivity and an excellent crosslinking effect and hence is a crosslinking agent component necessary for crosslinking the above-mentioned component (a1) at a high density. Furthermore, synthesizing the crosslinked fine particles using the crosslinking agent (a2) with three or more (meth)acryloyl groups enables a large number of radical-polymerizable ethylenic unsaturated groups derived from the crosslinking agent remaining on the surfaces and/or in the interior of the crosslinked fine particles.
In the present invention, when only a compound having two (meth)acryloyl groups is used as a crosslinking agent in place of the component (a2), crosslinked fine particles having a low crosslinking density tend to be obtained. Therefore, when these fine particles are dispersed in the compound (B) having at least one (meth)acryloyl group in the molecule, the component (B) infiltrates into the fine particles, so that the viscosity of the resulting resin composition tends to be extremely increased. In this case, the number of radical-polymerizable ethylenic unsaturated groups remaining in the crosslinked fine particles tend to be very small, so that it tends to be impossible to increase the curing rate of the curable composition that contains the crosslinked fine particles.
Specific examples of the component (a2) include (meth)acrylic acid esters such as trimethylolpropane tri(meth)acrylic acid ester, ethoxylated trimethylolpropane tri(meth)acrylic acid ester, propoxylated trimethylolpropane tri(meth)acrylic acid ester, glycerol tri(meth)acrylic acid ester, ethoxylated glycerol tri(meth)acrylic acid ester, tris(acryloxyethyl) isocyanurate, ditrimethylolpropane tetra(meth)acrylic acid ester, pentaerythritol tri(meth)acrylic acid ester, pentaerythritol tetra(meth)acrylic acid ester, dipentaerythritol penta(meth)acrylic acid ester, dipentaerythritol hexa(meth)acrylic acid ester, etc.; urethane poly(meth)acrylates obtained by adding a (meth)acrylate having a hydroxyl group (e.g. 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate and a caprolactone adduct thereof) to a trimer or higher-order oligomer of a diisocyanate compound (e.g. hexamethylene diisocyanate, isophorone diisocyanate, tolylene diisocyanate, xylylene diisocyanate, diphenylmethane dilsocyanate and hydrogenated diphenylmethane diisocyanate); and epoxy poly(meth)acrylates obtained by adding (meth)acrylic acid to a polyepoxy compound having three or more epoxy groups in the molecule, such as a trifunctional or higher-order polyfunctional phenolic novolak type epoxy resin, a trifunctional or higher-order polyfunctional cresol novolak type epoxy resin, pentaerythritol polyglycidyl ether, trimethylolpropane triglycidyl ether, triglycidyltris(2-hydroxyethyl) isocyanurate or the like. Among these compounds, when trimethylolpropane tri(meth)acrylic acid ester, ditrimethylolpropane tetra(meth)acrylic acid ester, pentaerythritol tri(meth)acrylic acid ester, pentaerythritol tetra(meth)acrylic acid ester, dipentaerythritol penta(meth)acrylic acid ester, dipentaerythritol hexa(meth)acrylic acid ester or the like are used, double bonds derived from the compound (a2) tend to be well left on polymerizing the compounds (a1) and (a2), which is desirable.
The above-exemplified compounds may be used either singly or in combination.
In the present invention, the proportions of the compounds constituting the crosslinked fine particles (A), i.e., the compound (a1) having one or two radical-polymerizable ethylenic unsaturated groups in the molecule and the compound (a2) having three or more (meth)acryloyl groups in the molecule are not particularly limited. The proportion of the component (a1) ranges preferably from 55 to 95 wt %, more preferably, 65 to 95 wt %, in the total proportion (100 wt %) of the component (a1) and the component (a2). The proportion of the component (a2) ranges preferably from 5 to 45 wt %, more preferably, 5 to 35 wt %.
When the proportion of the component (a2) relative to the component (a1) is less than 5 wt %, the crosslinking density of the crosslinked fine particles becomes low. Therefore, when the resulting fine particles are dispersed in the radical-polymerizable unsaturated compound (B), the component (B) infiltrates into the fine particles, so that the viscosity of the resulting resin composition tends to be extremely increased. When the proportion of the component (a2) relative to the component (a1) is more than 45 wt %, gelation tends to take place during the polymerization.
In the present invention, the crosslinked fine particles, component (A), can be obtained by polymerization by a well-known polymerization method. An emulsion polymerization method is especially preferable.
The emulsion polymerization method is not particularly limited. Examples of emulsion polymerization methods include mixing-in-one-lot polymerization method, monomer dropping method, pre-emulsion method, seed polymerization method, multi-stage (core/shell) polymerization method, etc.
When the above-exemplified emulsion polymerization method is adopted, the polymerization is preferably carried out with the use of an emulsifying agent in order to produce the crosslinked fine particles industrially.
Specific examples of emulsifying agent suitable for obtaining the crosslinked fine particles used in the present invention include nonionic surfactants such as polyethylene glycol nonylphenyl ether, polyethylene glycol dodecylphenyl ether, etc.; anionic surfactants such as sodium lauryl sulfate, sodium laurylbenzenesulfonate, sodium dodecylbenzenesulfonate, sodium dialkylsulfosuccinates, etc,; and reactive surfactants such as polyoxyethylene alkylphenyl ether acrylic acid esters, polyoxyethylene alkylpropenylphenyl ethers, polyoxyethylene alkylpropenylphenyl ether sulfuric acid ester ammonium salts, ammonium salt of xcex1-sulfo-xcfx89-(1-((nonylphenoxy)methyl)-2-(2-propenyloxy)ethoxy)-poly(oxy-1,2-ethanediyl), etc.
Among the above-exemplified emulsifying agents, the anionic surfactants superior in emulsifying capability are preferable. Radical-reactive anionic surfactants that can be incorporated into the fine particles are more preferable for improving the durability of a coating film.
The proportion of the emulsifying agent used is preferably 0.1 to 8 wt % based on the total weight of the component (a1), the component (a2) and pure water at the time of emulsion polymerization. Specifically, the following proportions are preferable: pure water 100 to 300 parts by weight, the total amount of the component (a1), and the component (a2) (=polymerizable monomers) 50 to 150 parts by weight, and the emulsifying agent 0.45 to 13 parts by weight.
The crosslinked fine particles (A) thus obtained are blended with the compound (B) after being dried by water removal.
The component (A) used in the present invention refers to one which is in a dried and pulverized state. The drying method is not particularly limited and includes a method comprising coagulation, washing, drying and then pulverization, a spray drying method, etc.
For example, when the curable resin composition of the present invention is utilized as an radiation curable resin composition, the spray drying method is preferred because it gives fine particles (A) having a small average particle diameter of aggregated particles, which tend to be easily dispersed when mixed with a resin composition.
The average primary-particle diameter of the cross-linked fine particles (A) used in the present invention ranges from 10 to 1,000 nm. The reason is as follows. When the average primary-particle diameter of the component (A) is less than 10 nm, the viscosity of the resulting resin composition tends to be greatly increased. When the average primary-particle diameter of the component (A) is more than 1,000 nm, the appearance of a cured coating film of the resulting resin composition tends to be unsatisfactory.
The especially preferable range of the average primary-particle diameter is 50 to 800 nm. The average primary-particle diameter ranges more preferably from 50 to 250 nm from the viewpoint of the transparency of a coating film.
In the present invention, the percentage of cubical expansion of the crosslinked fine particles (A) in methyl ethyl ketone at 25xc2x0 C. is not particularly limited. The percentage of cubical expansion is preferably 300% or less because when such fine particles are dispersed in the radical-polymerizable unsaturated compound (B), the viscosity of the resulting resin composition tends to be not extremely increased when the component (B) infiltrates into the fine particles. The percentage of cubical expansion is preferably, in particular, 250% or less.
In order to obtain the crosslinked fine particles (A) having a percentage of cubical expansion in methyl ethyl ketone at 25xc2x0 C. of 300% or less, the proportions of the compounds constituting the crosslinked fine particles (A), i.e., the ethylenic unsaturated compound (a1) and the compound (a2) having three or more (meth)acryloyl groups in the molecule are as follows: in the total proportion (100 wt %) of the component (a1) and the component (a2), the proportion of the component (a1) ranges preferably from 95 to 65 wt %, and the proportion of the component (a2) ranges from 5 to 35 wt %.
In the present invention, the percentage of cubical expansion (%) in methyl ethyl ketone of the crosslinked fine particles (A) is calculated by the following method.
The primary-particle diameter of crosslinked fine particles obtained by the above-mentioned emulsion polymerization method is measured at 25xc2x0 C. by a dynamic light scattering method, and the average particle diameter of the crosslinked fine particles is taken as R1. The dried and pulverized crosslinked fine particles (A) are re-dispersed in methyl ethyl ketone at 25xc2x0 C. and their average-particle diameter is measured by using the same system as above. This average particle diameter is taken as R2.
The method for dispersing the crosslinked fine particles (A) in methyl ethyl ketone is not particularly limited. The crosslinked fine particles (A) can be dispersed by the use of any dispersing machine such as a homodisperser, dissolver, three roll mill, ball mill or the like after being mixed with methyl ethyl ketone. The percentage of cubical expansion (%) in an organic solvent of the crosslinked fine particles is represented by V (%) in the following equation:
V=(R2)3/(R1)3xc3x97100
The amount of double bonds remaining in the dried and pulverized crosslinked-fine-particles (A) used in the present invention is preferably 0.01 mmol/g or more. When the amount of the remaining double bonds is less than 0.01 mmol/g, the curability of the resulting curable composition containing the crosslinked fine particles (A) dispersed therein tends to be not improved, which is not desirable. Although the method for determining the amount of the remaining double bonds is not particularly limited, a value determined by the following determination method is defined as the amount of the remaining double bonds in the present invention.
One gram of the crosslinked fine particles (A) obtained are accurately measured (the accurately measured amount is taken as x g), and then the crosslinked fine particles accurately measured, 20 g of water and 4 g of tetrahydrofuran (THF) are placed in a 200-ml flask and stirred for 30 minutes. To the resulting mixture are added 10 ml of a 0.1N KBrO3 aqueous solution and 5 ml of 6N HCl, immediately after which the flask was closed with a plug, followed by stirring in the dark for 5 minutes. Bromine is thus produced and added to double bonds remaining in the crosslinked fine particles. After the flask was allowed to stand in a dark room for 30 minutes, 5 ml of a 15 wt % KI aqueous solution is added into the flask while cooling the flask with ice water, and the resulting mixture is stirred for 5 minutes. By this stirring, non-added bromine is replaced with iodine. The iodine produced is titrated with a 0.1N Na2S2O3 aqueous solution. The titration end point is a point at which the color of the dark-brown liquid changes to colorless or yellow. The amount of the remaining double bonds is determined from the titer according to the following equation:       Amount    ⁢          xe2x80x83        ⁢    of    ⁢          xe2x80x83        ⁢    remaining    ⁢          xe2x80x83        ⁢    double    ⁢          xe2x80x83        ⁢    bonds    ⁢          xe2x80x83        ⁢          (        ⁢    mmol    ⁢          /        ⁢    g    ⁢          )        =            1      2        xc3x97          [                        (                      titer            ⁢                          xe2x80x83                        ⁢            for            ⁢                          xe2x80x83                        ⁢            blank                    )                -                  (                      titer            ⁢                          xe2x80x83                        ⁢            for            ⁢                          xe2x80x83                        ⁢            sample                    )                    ]        xc3x97    0.1    xc3x97    f    xc3x97          (              1        /        x            )      
wherein the titer for blank is the titer (ml) of the 0.1N Na2S2O3 aqueous solution measured in the case of not using the sample (the fine particles) in the above determination method; the titer for sample is the titer (ml) of the 0.1N Na2S2O3 aqueous solution measured in the case of using the sample (the fine particles) in the above determination method; f is a factor for 0.1N Na2S2O3; and x is the amount (g) of the sample (the fine particles) accurately measured.
The glass transition temperature (Tg) of the dried and pulverized crosslinked-fine-particles (A) used in the present invention is preferably 100xc2x0 C. or higher. When the glass transition temperature (Tg) is lower than 100xc2x0 C., the curability of the resulting curable composition containing the crosslinked fine particles (A) dispersed therein tends to be not improved, which is not desirable. A method for measuring the Tg is not particularly limited. In the present invention, the dried and pulverized crosslinked-fine-particles (A) are placed directly on a glass stage, and the Tg is defined as a thermal and mechanical value determined from a change of the thermal expansion coefficient by using the TMA method.
The resin composition of the present invention is obtained by blending by dispersion the crosslinked fine particles (A) with the component (B). A method for dispersing the component (A) in the component (B) to blend them is not particularly limited. The component (A) can be dispersed in component (B) by the use of any dispersing machine such as a homodisper, dissolver, triple-roll mill, ball mill or the like after being mixed with the component (B).
In the present invention, the compound (B) having at least one (meth)acryloyl group in the molecule is used as a dispersion medium for the component (A).
As specific examples of the component (B), the (meth)acrylic acid esters mentioned above as specific examples of the component (a1), and the component (a2) can be used. In addition to these, there can be mentioned, for example, polyester poly(meth)acrylates obtained by the reaction of a polybasic acid (e.g. phthalic acid and adipic acid), a polyhydric alcohol (e.g. ethylene glycol, hexanediol, poly(ethylene glycol)s, poly(tetramethylene glycol)s) and (meth)acrylic acid or its derivative; epoxy poly(meth)acrylates obtained by reacting a glycidyl ether compound (e.g. bisphenol A diglycidyl ether and ethylene glycol diglycidyl ether) with a (meth)acrylic acid or its derivative; and urethane poly(meth)acrylates obtained by reacting an isocyanate compound (e.g. hexamethylene diisocyanate, isophorone diisocyanate, tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, and hydrogenated diphenylmethane diisocyanate) with a (meth)acrylate having a hydroxyl group (e.g. 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate).
These may be used either singly or in combination.
The proportions of the crosslinked fine particles (A) and the compound (B) are as follows: in the total proportion (100 wt %) of the component (A) and the component (B), the proportion of the component (A) ranges from 5 to 50 wt %, and the proportion of the component (B) ranges from 50 to 95 wt %.
When the proportion of the component (A) is more than 50 wt %, the resulting resin composition has a high viscosity, so that its coatability tends to be poor. When the proportion of the component (A) is less than 5 wt %, the curability and low shrink properties intended according to the present invention tend to be insufficient.
It is preferable to incorporate radical polymerization initiators (C) such as photopolymerization initiators (c1), thermal polymerization initiators (c2) and the like into the curable resin composition of the present invention.
Specific examples of the photopolymerization initiators (c1) include benzophenone, 4,4-bis(diethylamino)benzophenone, t-butylanthraquinone, 2-ethylanthraquinone, and thioxanthones (e.g. 2,4-diethylthioxanthone, isopropylthioxanthone and 2,4-dichlorothioxanthone); acetophenones such as diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyl dimethyl ketal, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-2-morpholino(4-thiomethylphenyl)propan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone, etc.; benzoin ethers such as benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, etc.; acylphosphine oxides such as 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, etc.; methylbenzoyl formate; 1,7-bisacrydinylheptane; 9-phenylacridine; etc.
These photopolymerization initiators (c1) may be used singly or in combination and are incorporated into the present resin composition comprising the component (A) and the component (B), in a proportion of preferably 0.01 to 20 parts by weight, in particular, 0.1 to 10 parts by weight, per 100 parts by weight of the resin composition.
In addition, if necessary, well-known photosensitizers such as methyl 4-dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate, amyl 4-dimethylamino-benzoate, 4-dimethylaminoacetophenone, etc. may be incorporated into the curable resin composition of the present invention.
Specific examples of the thermal polymerization initiators (c2) include organic peroxides such as methyl ethyl ketone peroxide, benzoyl peroxide, dicumyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide, t-butyl peroxyoctoate, t-butyl peroxybenzoate, lauroyl peroxide, etc.; azo compounds such as azobisisobutyronitrile, etc.; and redox polymerization initiators obtained by combining amines (e.g. N,N-dimethylaniline and N,N-dimethyl-p-toluidine) with any of the above-mentioned peroxides. The 10-hours half-life temperature of these thermal polymerization initiators (c2) is preferably 100xc2x0 C. or lower. If a thermal polymerization initiator having a 10-hours half-life temperature of higher than 100xc2x0 C. is used, the curing rate tends not to be increased.
If necessary, metal soaps such as cobalt naphthenate, manganese naphthenate, nickel octylate, etc. may also be used.
These thermal polymerization initiators (c2) may be used either singly or in combination and are incorporated into the resin composition comprising the component (A) and the component (B), in a proportion of preferably 0.001 to 10 parts by weight, in particular, 0.01 to 5 parts by weight, per 100 parts by weight of the resin composition.
In addition, well-known additives such as mold release agents, lubricants, plasticizers, antioxidants, ultraviolet absorbers, flame retardants, flame-retarding assistants, polymerization inhibitors, fillers, organic solvents usable in the present invention, pigments, dyes, silane coupling agents, etc. may be properly used depending on their purpose, in the resin composition and crosslinked-fine-particle dispersion type curable resin composition of the present invention.
The curable resin composition of the present invention is useful as a composition substantially free of water and solvents. The viscosity of said composition is preferably 10 Paxc2x7s or less at 25xc2x0 C., more preferably 5 Paxc2x7s or less at 25xc2x0 C., from the viewpoint of work-efficiency. A curable resin composition having a viscosity of more than 10 Paxc2x7s at 25xc2x0 C. requires heating in some cases at the time of coating or printing in order to reduce the viscosity and, thus, tends to result in the deterioration of the productivity. Moreover, even if the application or printing with such composition is possible the appearance of the resulting coating or print tends to be unsatisfactory, which is not desirable.
The curable resin composition of the present invention can be used in any of the fields of molded articles, adhesives, coating materials, inks, resins for stereo lithography, photoresists, etc. The method for curing said resin composition is not particularly limited, and the resin composition can be cured by various curing methods well known and conventionally used in the fields mentioned above.
In particular, the resin composition causes only a slight viscosity increase when added to a dispersion medium, it is excellent in curability and can have low shrink properties. Therefore, the resin composition can exhibit its performance characteristics to the utmost when used as a radiation curable resin which can be used, for example, for film coatings and wood coatings and in printing inks.